1. Field of the Invention
The present invention relates to an improvement in a process for obtaining color photographic images by reversal color photographic processing. Particularly, it relates to an improvement in the fogging bath used in reversal color photographic processing.
2. Description of the Prior Art
Reversal color photographic processing essentially involves the following four steps.
(1) First development. PA1 (2) Fogging treatment. PA1 (3) Color development. PA1 (4) Silver removal. PA1 R.sub.2 is a hydrogen atom, an alkyl group containing 1 to 4 carbon atoms, --(CH.sub.2).sub.n COOM' or a phenyl group; PA1 R.sub.3 is a hydrogen atom or --COOM'; PA1 M and M', which may be the same or different, each is a hydrogen atom, an alkali metal atom or an ammonium group; PA1 m is 0 or 1; and PA1 n is 1 to 4. PA1 R.sub.2 is a hydrogen atom, an alkyl group containing 1 to 4 carbon atoms (such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group and a tert-butyl group), --(CH.sub.2).sub.n COOM' or a phenyl group; PA1 R.sub.3 is a hydrogen atom or --COOM'; PA1 M and M', which may be the same or different, each is a hydrogen atom, an alkali metal atom (such as Na, K, Li) or an ammonium group; PA1 m=0 or 1; and PA1 n=1 to 4. It is preferred for R.sub.2 to represent a hydrogen atom, a methyl group or a carboxymethyl group.
In the first development in the above-described processing, silver halide having a latent image formed by exposure to light is developed. In the color development, the silve halide which was not developed in the first development is developed in the presence of color couplers to form color images. In the silver removal, developed silver formed in the first development and the second development is oxidized and removed from the photographic light-sensitive material by a fixing agent. The fogging treatment means processing the silve halide grains to provide development nuclei therein so that the silver halide which was not developed in the first development is sufficiently reduced to form dye images.
In order to carry out the fogging processing, although sufficient uniform exposure of the photographic material to light is sometimes used, chemical fogging is often carried out by processing the photographic material using a fogging bath containing a fogging agent or incorporating a fogging agent in the color developing solution. In the latter case, the two steps of the fogging treatment and the color development are carried out at the same time. As chemical fogging agents, alkali metal borohydrides are described in U.S. Pat. No. 2,984,567 and ionic ammonium borohydrides are described in U.S. Pat. No. 3,246,987.
However, since alkali metal borohydrides are unstable in aqueous solutions, the fogging effect of the fogging bath or the color developing solution including the alkali metal borohydrides disappears with the lapse of time. Although the amino borane compounds described in U.S. Pat. No. 3,246,987 do not have this defect, much care must be taken in handling these compounds because they are quite poisonous.
A fogging bath or a color developing solution containing stannous aminopolycarboxylic acid chelate compounds or stannous organic phosphonic acid chelate compounds or stannous organic phosphonic acid chelate compounds is described in U.S. Pat. Nos. 3,658,535 and 3,617,282.
However, these fogging agents are not sufficiently stable in aqueous solutions and are decomposed in the fogging bath or the color developing solution. Consequently, their fogging function deteriorates within a comparatively short period of time even if they are added to the solution in an excess amount.